Abstract The aim of the study was to determine the hybridity of the F₁ generation of Vaccinium cf. uliginosum × V. vitis-idaea × Oxycoccus macrocarpus created through the consecutive crossing of some common berry species of the family Ericaceae (bog whortleberry, cowberry and marsh cranberry) at the tetraploid level. Certain aspects of phenology and morphometric parameters of vegetative organs of the supposed hybrid and parent plants were analysed using traditional methods of comparative analysis. Molecular genetic assay, including random amplification of polymorphic DNA, simple sequence repeat and sequencing, were also used. Comparison of the phenological and morphometric features of the experimental plant and its parents allows suggesting that in the combination of crossing of (V. uliginosum × V. vitis-idaea) × O. macrocarpus (the cultivar Searles), a three-species hybrid was created. The allelic variants, specific for V. uliginosum, V. vitis-idaea and O. macrocarpus, were detected in the V. cf. uliginosum × V. vitis-idaea × O. macrocarpus genotype. A next-generation sequencing approach is suggested for estimating the share of the genomes of Vaccinium spp. in the formation of the interspecies hybrid.